Figure 3-3 Air Mass Symbology

AVIATION WEATHER

CHAPTER THREE

Naturally, moist air masses will have a greater potential for producing clouds and precipitation

than dry air masses. Most importantly, though, its temperature indicates the stability of the air

mass. Warm air masses bring stable conditions, while cold air masses are inherently unstable.

This temperature classification is relative to the surface beneath it. An air mass with a

temperature of 90F over a surface with a temperature 100F is classified as cold.

A maritime air mass would be reclassified to continental when precipitation over land occurs. A

continental air mass would be reclassified to maritime if evaporation over water occurs

(Figure 3-2).

Moisture Content

Symbol

Surface

(Related to Dew point Temperature)

Maritime

High

Continental

Low

Figure 3-2 Source Region Surface

These symbols are combined to describe air masses as follows (Figure 3-3)

Symbol

Source Region and Surface

Continental Arctic

Continental Polar

Maritime Polar

Maritime Tropical

Continental Tropical

Equatorial

Figure 3-3 Air Mass Symbology

Air masses are also classified by temperature. An air mass leaving its source region will

generally be warmer than the surface over which it is flowing if it is moving north, or colder than

the surface over which it is flowing if it is moving south. If the air mass is warmer than the

surface, it is cooled by contact with the cold ground, becomes more stable, and is called a warm

air mass (Figure 3-3). If the air mass is colder than the surface over which it is moving, it is

heated from below, resulting in convective currents and instability and is called a cold air mass.

305.

FRONTAL SYSTEMS

A front is an area of discontinuity that forms between two contrasting air masses when they are

adjacent to each other. A front can be thought of as a border, boundary, or line between the air

masses. These air masses must have sufficiently different temperature and moisture properties,

the defining characteristics of an air mass, otherwise there would be little reason to distinguish

between them. Since air masses cover many thousands of square miles, the boundary between

Mechanics of Frontal Systems 3-3